Barium Copper Silicate-Based Low-Permittivity Microwave Dielectric Ceramics And Their Application For LTCC

Microwave dielectric ceramics play an important role in passive electronic components.With the expansion of wireless communication to high frequencies,microwave dielectric ceramics with low dielectric constant and LTCC have been given great attention by academia and industry.This paper closely focused on Barium Copper Silicate-based low-?r microwave dielectric ceramics.The phase composition,crystal structure evolution and microwave dielectric properties of Barium Copper Silicate-based ceramics are systematically investigated.Moreover,a series of Barium Copper Silicate-based LTCC materials were prepared by adding fluoride composite sintering aids,and the co-firing characteristics between the LTCC matrix and the silver electrode were studied.The phase evolution process of Barium Copper Silicate-based ceramics was studied by solid-state reaction method.The synthesis temperatures of BaCu₂Si₂O₇,BaCuSi₂O₆ and BaCuSi₄O₁₀ were 950?,1050?and 1075?,respectively.Moreover,the decomposition temperatures of BaCu₂Si₂O₇,BaCuSi₂O₆ and BaCuSi₄O₁₀ were 1075?,1100?and1200?,respectively.It is clarified that BaCuSi₂O₆ in Barium Copper Silicate is the preferential phase,instead of BaCu₂Si₂O₇ reported in the literature.The final evolution direction of the phase is determined by the proportion of elements.The microwave dielectric properties of Ba_1-xSr_xCu₂Si₂O₇ and BaCu_2-xCo_xSi₂O₇ solid solutions are investigated using equivalent ion replacement methods.The solid solubility of Ba_1-xSr_xCu₂Si₂O₇ is x=0.35.When x?0.40,impurity phases such as BaCuSi₄O₁₀ and BaCuO₂ were detected.With the increasing of Sr²⁺content,the?_r of Ba_1-xSr_xCu₂Si₂O₇increased monotonously from 8.29 to 8.50,and the quality factor Q×f increased to the maximum value 51515 GHz at x=0.20 and then decreased.The temperature coefficient of resonant frequency?_f shown an opposite trend to the Q×f.Optimum microwave dielectric properties of Ba_1-xSr_xCu₂Si₂O₇ solid solution were ontained when x=0.20 with?_r=8.43,Q×f=51515 GHz and?_f=-29.70 ppm/?.The solid solubility of BaCu_2-xCo_xSi₂O₇ is between x=0.15 and 0.20.When x?0.20,impurity phases such as Si O₂ was detected.The?_r,Q×f and|?_f|of BaCu_2-xCo_xSi₂O₇ increase with the increase of Co²⁺content.Optimum microwave dielectric properties of BaCu_2-xCo_xSi₂O₇ solid solution were obtained when x=0.15 with?_r=8.45,Q×f=58958 GHz and?_f=-34.42 ppm/?.BaCuSi₂O₆ has a near-zero?_f value and its microwave dielectric properties were?_r=8.45,Q×f=31424 GHz and?_f=+0.36 ppm/?.The solid solubility of Ba_1-xSr_xCuSi₂O₆ was x=0.25 and impurity phases such as BaCu₂Si₂O₇ and BaCuSi₄O₁₀ were detected when x?0.30.The?_r of Ba_1-xSr_xCuSi₂O₆ decreased from 8.45 to 8.12 due to the decreasing of the ion polarization in unit cell.The Q×f of Ba_1-xSr_xCuSi₂O₆ was closely related to the lattice energy and both of them reached their maximum values at x=0.20.?_f depended on the stability of the[CuO₄]and[Si₄O₁₂]in Ba_1-xSr_xCuSi₂O₆.In the range of x=0?0.20,the stability of[CuO₄]decreased slightly and?_f changed from positive to negative.As for x=0.25,?_f decreased significantly due to the stability of the[Si₄O₁₂]ring decreased.The excellent microwave dielectric properties of Ba_1-xSr_xCuSi₂O₆ solid solution were obtained at x=0.20 with?_r=8.25,Q×f=47616 GHz and?_f=-9.61 ppm/?.Microwave dielectric properties of Ba_1-xSr_xCuSi₄O₁₀,Sr_1-xCa_xCuSi₄O₁₀ and Sr Cu_1-xCo_xSi₄O₁₀ solid solutions were studied.With the increasing of x value,the microwave dielectric properties of Ba_1-xSr_xCuSi₄O₁₀ changed monotonously.The dielectric constant decreased from 6.03 to 5.59,the quality factor changed from 49952 GHz to 82252 GHz and the temperature coefficient of resonant frequency decreased from-18.00 ppm/?to-41.34ppm/?.The solid solubility of Sr_1-xCa_xCuSi₄O₁₀ and Sr Cu_1-xCo_xSi₄O₁₀ are 0.20 and 0.15,respectively.The stability of the crystal structure for Sr_1-xCa_xCuSi₄O₁₀ and Sr Cu_1-xCo_xSi₄O₁₀were reduced and the quality factor were deteriorated.Sr CuSi₄O₁₀ has a low dielectric constant(5.59)and a high-quality factor(82252 GHz),which made it a good candidate for millimeter wave devices.Barium Copper Silicate-based LTCC materials were prepared by adding fluoride composite sintering aids.This series of LTCC materials could be co-fired with silver below900?.After sintering at 875?for 3 hours,the microwave dielectric properties of BaCuSi₂O₆-3 wt%LMS were?_r=8.16,Q×f=24351 GHz,?_f=-9.74 ppm/?;microwave dielectric properties of BaCuSi₄O₁₀-3 wt%LMS were?_r=6.15,Q×f=31389 GHz,?_f=-20.30 ppm/?and microwave dielectric properties of Sr CuSi₄O₁₀-3 wt%LMS were?_r=5.63,Q×f=44710 GHz,?_f=-33.87 ppm/?.